DE69717894T2 - Method and device for separating a material web on a weakening line - Google Patents

Description

This invention relates generally to breaking a web along spaced lines of weakness. More particularly, the invention relates to methods and apparatus for breaking continuous webs, such as plastic webs, in the manufacture of plastic bags or groups of plastic bags, or other workpieces, and for layering or otherwise accumulating the workpieces.

This invention relates to new devices and methods for breaking a web along spaced lines of weakness. Devices for breaking a web are known in the art. Gietman et al. U.S. Patent 5,362,013 discloses a device which breaks a plastic web along spaced lines of perforation. The Gietman et al. device feeds the web through a webbing assembly 202 to a rotating drum assembly 203. The rotating drum assembly 203 includes a rotating drum 225 and stationary guide rollers 217-222. As shown in Fig. 3 of Gietman et al., the rotating drum 225 rotates in a counterclockwise direction so that spools 226 and 227 stretch and thus break the web. Stationary guide rollers 217-222 guide the web along the desired path. The rotating drum 225 also takes up slack in the web caused by the greater speed of the web through the intake assembly 202 as compared to the speed through the wind-up assembly 204.

In a commercially available embodiment of the Gietman et al. apparatus, the rotary drum 225 has a diameter of at least 12.7 cm (5"). The drum has a first gap element of at least about 2.54 cm (1") between the feed assembly and the rotary drum 225. and a second gap element of about 7.6 cm (3") between the rotary drum 225 and the nip formed by the rollers 230, 231 of the windup assembly 204. The total length of the gap along the machine direction between the guide rollers 210 and rollers 230, 231 is about 22.8 cm (9"). The rollers 217-222 are used to support the web and to ensure that the web travels along the desired path over the length of the nip. Furthermore, the length of the gap of 22.8 cm (9") directly relates to the overall length of the windup apparatus 200 of Gietman et al.

Cutting of laminated strips is taught in GB-A-1,501,690. In particular, a web of plastic film is cut partially at its edge by a sharp-edged knife rotating on a holder. The web of plastic film is then torn the rest of the way across the width, since the knife cut only extends a very short distance across the width of the web. In addition, the knife serves to cause the orientation of sheets from underlap to overlap. The actual separation of the sheets is accomplished by a snapping action at a nip between two pulling or separating rollers.

US-A-4,623,081 discloses a separating device for continuous forms. The separating device separates sheets of a continuous form having transverse weakened lines. The continuous form is transported along a feed path by the device which includes a movable separator bar extending closer to the feed path. The device provides a clamping element operable to clamp the continuous form with a weakened line aligned directly over the path of travel of the separator bar. A pair of cam and linkage members are arranged to guide the separator bar through the feed path while the form is clamped. Said bar is initially arranged to be inclined with respect to the feed path. As the cam and linkage members move one revolution, the separator bar moves upwardly through the continuous form to separate a sheet from the continuous form at one of the weakened lines. The separator bar then moves back to its initial rest position. Because of the inclination, the leading edge of the separator bar does not contact the entire width of the continuous form, but instead begins by contacting the continuous form at one end thereof and then progressively separates the form across toward the other end as the bar continues its upward movement.

GB-A-2,137,597 discloses a method and apparatus for separating laminated sheets from a web, wherein adjacent sheets have their edge end portions in an overlapping relationship. As the web is transported through the apparatus, an overlap region is detected by a sensor unit and a tear-initiating intermittently operable blade is then caused to make a short cut in an edge adjacent to the overlap region. Thereafter, the web enters a nip between tear rollers 1 which, due to their peripheral speeds which are greater than the web speed of the web, promote the separation of a sheet from the web, the separation taking place transversely to the web in the tear initiation step.

According to a first aspect of the invention, there is provided an apparatus for separating a workpiece from a web of continuous material at lines of weakness transverse to the width (W) as the web moves and at spaced intervals along the length of the web and at least partially through a thickness of the web, the apparatus comprising first and second driven rollers defining a first nip for receiving and transporting the web therethrough, third and fourth rollers defining a second nip for initially receiving and then transporting the workpiece separated from the web through the second nip, and a controller for controlling the drive of the web through the first nip and for driving the web and the workpiece, once separated from the web, through the second nip, the apparatus (10) being characterized by:

a breaker bar assembly disposed between the first gap and the second gap, the breaker bar assembly including means for separating the workpiece from the web at a first line of weakness, the separating means comprising at least one breaker bar, the at least one breaker bar extending substantially transversely to the width of the web to provide assistance in cleanly separating the workpiece from the web at the first line of weakness when a drive device of the breaker bar assembly directs the at least one breaker bar horizontally downward into full width contact against and through the web, the at least one breaker bar having a generally arcuately shaped cross section with a blunt leading edge for contact with the web at a line of contact displaced from the first line of weakness and operable to separate the workpiece from the web at the first line of weakness rather than cutting the web at the line of contact.

According to another aspect of the invention, there is provided a method for severing a continuous web of material (20) during movement of the web at lines of weakness transverse to the width (W) and at spaced intervals along the length of the web, the method comprising the steps of: providing an apparatus having first and second driven rollers defining a first nip for receiving and transporting the web therethrough, third and fourth rollers defining a second nip for initially receiving and transporting the workpiece separated from the web through the second nip, and a controller for controlling the driving of the web through the first nip and for driving the web and the workpiece, once separated from the web, through the second nip, the method being characterized by the steps of:

Providing a breaker bar assembly having means for separating the web at a first line of weakness from the lines of weakness, the breaker bar assembly being disposed between the first gap and the second gap;

providing the separating device with the at least one breaker bar extending substantially across the width of the web and movable to cleanly separate the workpiece from the web at the first separation line, the at least one breaker bar having a generally arcuately shaped cross-section with a blunt leading edge for contact with the web at a contact line displaced from the first line of weakness;

Activating the drive mechanism of the breaker bar assembly to bring the at least one breaker bar into a substantially horizontal position directed downwards into full width contact against and through the web so that the blunt leading edge of the generally arcuately shaped cross-section contacts the web at a contact line that is displaced from the first line of weakness, thereby separating the workpiece from the web at the first line of weakness as the web moves, rather than cutting the web at the contact line.

Some of the objects of the invention are achieved in a first family of embodiments comprising an apparatus for breaking a web having a length and a width, the web having spaced lines of weakness therein and traveling in a predetermined general direction. The apparatus includes first and second driven rollers forming a first nip. The first nip receives the web and transports it through the first nip. The breaker bar assembly includes at least first and second breaker bars and a drive device that drives the breaker bars in a downward translational direction. Third and fourth driven rollers downstream of the breaker bar assembly form a second nip that receives the web and transports the web through the second nip. A controller controls the drive of the driven rollers of the first and second nips via the drive device and directs at least one breaker bar into engagement with the web, wherein movement of the breaker bar in a downward direction causes breaking of the web.

In some embodiments, the breaker bar assembly includes a first rotating member having at least first and second breaker bars. The first rotating member is driven by a drive device to incrementally and intermittently rotate the breaker bars against the web with sufficient force to cause the web to break.

The breaker bar assembly may further comprise a second rotating member including at least third and fourth breaking bars. In this embodiment, the web has first and second opposing edges. The first rotating member is mounted adjacent the first edge. The second rotating member is mounted adjacent the second edge. Each breaking bar rotates in a closed path substantially perpendicular to the direction of travel of the web, the paths extending transversely to the width of the web.

The drive device preferably has a servo motor which drives the first and second rotation elements.

The crowbar assembly may further include first and second belts, preferably synchronous belts, and a gear used by the servo motor to drive the first and second rotating members. Any synchronous drive may be used for the first and second belts. Synchronous belts are preferred, although synchronous chains and the like may also be used.

Preferably, the breaker bars are arranged in a common plane extending transversely to the web. The controller controls the first and second rotary elements in opposite directions and synchronizes the rotary elements so that each corresponding breaker bar on the first rotary element cooperates with a corresponding breaker bar on the second rotary element transversely to the surface of the web so that the corresponding breaker bars simultaneously engage and break the web. The respective cooperating breaker bars are preferably substantially aligned with each other when the corresponding breaker bars jointly engage and break the web. The cooperating Crowbars prefer to define equal and opposite angles to the track.

In preferred embodiments, the breaker bars travel in paths substantially perpendicular to the direction of travel of the web when engaging the web.

In some embodiments, the crowbar assembly includes a first belt supporting at least first and second of the crowbars. The first belt is mounted on a first guide device and is driven by the drive device to incrementally and intermittently move the crowbars along a first elongated closed path. The crowbar assembly may include a second belt supporting at least third and fourth crowbars. The second belt is mounted on a second guide device and is driven by the drive device to incrementally and intermittently rotate the third and fourth crowbars along a second elongated closed path. The first belt is mounted adjacent the first edge. The second belt is mounted adjacent the second edge. Each belt is preferably a timing belt and each guide device is preferably a corresponding timing pulley.

It is preferred that major portions of the respective first and second longitudinal paths extend in straight lines, substantially perpendicular to the direction of travel of the web, preferably parallel to each other. Preferably, the breaker bars on the first belt travel in a plane together with the corresponding breaker bars on the second belt. In this embodiment, the control drives the first and second belts in opposite directions, and synchronizes the travel of the breaker bars along the first and second paths so that corresponding pairs of crowbars jointly grasp and break the path.

Preferably, the web has spaced apart lines of weakness extending transversely thereto defining respective bags in the web. The apparatus may further include a sensor which detects each line of weakness in the web.

In a layering mode of operation, the controller operates the breaker bar assembly to break the web in response to each detection of a line of weakness by the sensor, with each break of the web at each line of weakness producing a single workpiece. In this layering mode, third and fourth driven rollers are operated at a slower line speed than the first and second driven rollers, thereby layering or overlapping the workpieces between the nips. Thus, after each break at a line of weakness, a leading portion of the remainder of the web is placed on a trailing portion of the next successive downstream workpiece between the first and second nips.

The invention further contemplates driving the corresponding breaker bar in a preferably downward translational motion through the web, wherein each driving of the breaker bar assembly against the web entails engagement between the breaker bar assembly and the web at only a single line transverse to the width of the web. The engagement causes the web to break at a line of weakness between at least one breaker bar and the first gap.

In some embodiments, the crowbar assembly includes at least first and second crowbars configured to travel along first and second elongated closed paths, a first of the breaker bars being driven in a first substantially rectilinear direction along a first path segment into stretching engagement with the web at a first location along the length of the path, while a second of the breaker bars being driven in a second opposite substantially rectilinear direction along a second path segment into stretching engagement with the web at a second location spaced from the first location along the length of the path. The combined stretching engagements of the first and second breaker bars break the web. Each of the breaker bars moves in a corresponding rectilinear direction prior to engagement with the web, during subsequent stretching engagement with the web, and after the web breaks.

In some embodiments, the straight path segment has a spacing of at least about 10 cm (4") in each direction.

In preferred embodiments, the second path segment is spaced from the first path segment by a distance of no more than 3.8 cm (1.5"), preferably about 0.63 and 2.54 cm (0.24 and 1"). The first and second path segments may comprise first and second portions of a single elongated closed path.

In some embodiments, the breaker bar assembly includes a first drive belt mounted on a first guide device and disposed adjacent the first edge of the track. The breaker bar assembly may further include a second drive belt mounted on a second guide device and disposed adjacent the second edge of the track. Each breaker bar is preferably attached to both the first and second Drive belt and extends transversely to the track. The second belt drive and the second guide device are preferably aligned transversely to the track, to the first drive belt and to the first guide device. The drive device drives the first and second belts together and thereby guides the crowbars along the corresponding paths.

In some embodiments in which the first drive belt is mounted on the first guide device adjacent the first edge of the web and the second drive belt is mounted on the second guide device adjacent the second edge of the web, the first and third upwardly driven breaker bars are mounted on respective first and second belts in substantial alignment with each other. Second and fourth downwardly driven breaker bars are mounted on respective first and second drive belts in substantial alignment with each other such that the breaker bars travel on each belt in respective upward and downward rectilinear directions before engaging the web.

In some embodiments, the gap between the web drive assembly and the gap subassembly is less than 7.6 cm (3"). Preferably, the gap is between about 2.54 and 5.1 cm (1 and 2").

In preferred embodiments, the breaker bars engage the web and apply a take-up force across the width of the web, take up slack in the web, and continue to take up slack before breaking the web.

The invention further contemplates a method for breaking a web at spaced lines of weakness in the web. The method comprises transporting the web through a nip formed between first and second rollers, pulling the web through a nip formed by third and fourth rollers and through a breaker bar assembly between the first and second nips, engaging a line of weakness and driving at least one of the breaker bars in a downward direction so as to engage the web and break the web at the line of weakness. Breaking the web produces a separate workpiece having a trailing portion and correspondingly producing a leading portion of the remainder of the web. The breaker bar assembly includes at least first and second breaker bars and a drive device driving the breaker bars.

In preferred embodiments, the method includes incrementally and intermittently rotating first and preferably second rotary elements in response to successive signals from the controller in closed paths substantially perpendicular to the direction of travel of the web and extending transversely to the width of the web.

In some embodiments, the method includes advancing a first drive belt and incrementally and intermittently advancing at least first and second breaker bars along a first elongated closed path. At least third and fourth breaker bars on a second drive belt may be cooperatively advanced incrementally and intermittently along a second elongated closed path.

In some embodiments, the breaker bars travel in path segments substantially perpendicular to the direction of travel of the web and extend during and before or after the engagement with the track or both across the width of the track.

The invention further includes a method of breaking a web which includes driving a first of the breaker bars in a first substantially rectilinear direction along a first path segment into stretching contact with the web at a first location along the length of the web while driving a second of the breaker bars in an opposite substantially rectilinear direction along a second path segment into stretching contact with the web at a second location along the length of the web. The combined stretching contacts of the breaker bars break the web at the respective lines of weakness.

In some embodiments, the method includes detecting each line of weakness, and only when the last of a predetermined number of lines of weakness has been detected, breaking the web at the last line of weakness so detected, if the last line of weakness is downstream of the first gap.

In some embodiments, the method includes detecting each line of weakness and breaking the web at each detected line of weakness, wherein breaking the web at a line of weakness produces a single workpiece representing a single bag.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a representative side view of a first embodiment of the strip processing machine of the invention.

Fig. 2 is a representative front view of the break bar assembly at 2-2 of Fig. 1.

Fig. 3 is a representative front view of a second embodiment of the breaker bar assembly.

Fig. 3A shows a modified version of the embodiment of Fig. 3.

Fig. 4 is a representative side view of the embodiment of Fig. 3 in a belt processing machine of the invention.

Fig. 5 is a representative enlarged partial side view of a fragment of a third embodiment of the invention.

Fig. 6 is a representative top view of the embodiment of Fig. 5.

Figure 6A is a front view of a preferred drive system for the embodiment of Figure 5.

Fig. 7 is a plan view of a fourth embodiment of the invention.

Figs. 8A and 8B are representative top and side views of a fifth embodiment of the invention.

The invention is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in different ways. It is also to be understood that the terminology and wording used herein is for the purpose of description and illustration only and is not limiting. should be considered. Like reference numerals are used to designate like components.

Fig. 11 illustrates a strip processing machine which includes a tension roller assembly 12, a web drive assembly 14, a breaker bar assembly 16 and a take-up assembly 18.

Substantially the entire tape processing machine 10 of Fig. 1, with the exception of the breaker bar assembly 16, is similar to the machine described in Gietman et al., U.S. Patent 5,326,013, and is hereby incorporated by reference in its entirety. The web 20 has a width "W" (Figs. 6 and 7) and a continuous length, and travels in the direction shown by arrow 21.

Referring again to Fig. 1, the tension roller assembly 12 receives the web from a web source (not shown). Within the tension roller assembly 12, a pair of rollers 22, 24 help control the tension on the web 20. A position sensor (not shown) associated with the tension roller 24 sends position signals to an electrical controller 26 at closely spaced intervals. The controller 26 uses the position signals to make constant adjustments to the speed at which the web 20 is drawn into the machine 10 to keep the tension roller 24 generally in the middle of its range of travel.

The tension roller assembly 12 includes a weak line sensor 28. The sensor 28 detects spaced weak lines, such as perforations in the web 20 and provides a signal to the electrical controller 26 each time a weak line is detected. A variety of sensors are available for detecting weak lines. For example, a pair of electrodes (not shown) in a cooperating relationship above and below the web 20. A voltage may be applied between the electrodes and the web. The voltage creates an electrical arc between the electrodes when a perforation passes the electrodes. Multiple electrodes may be placed at multiple locations across the web 20. Sensed signals are sent to the electrical controller 26 which controls various elements of the belt processing machine.

The belt drive assembly 14 includes first and second rollers 30 and 32 which are urged against each other, thus defining a first gap 34 therebetween. A carrier belt 44 is stretched thereover and extends in a first path over rollers 30, 38 and 36. A carrier belt 46 is stretched and extends in a second path over rollers 32, 40 and 42. Rollers 38 and 40 are slightly spaced apart from each other. Likewise, carrier belts 44 and 46 are spaced apart from each other at rollers 38 and 40. Rollers 38, 40 and carrier belts 44, 46 provide guiding support for the web at rollers 38, 40, but do not provide a speed controlling gap such as at gap 34.

The carrier belts 44 and 46 are preferably made of nylon and another suitable polymer or rubber. The carrier belts 44 and 46 are preferably full-width carrier belts, but may have separate cords or strands in recesses (not shown) in their respective guide rollers. The carrier belts 44 and 46 guide the web 20 through the web drive assembly 14.

The drive device 48 drives the drive belt 50, thus driving the roller 33, which in turn drives the roller 30. The drive device 48 can be a servo motor, a standard AC motor or the like. The electrical control 26 controls the speed of the drive device 48 and thus the speed at which the web 20 is pulled into the web drive assembly 14 by the roller 30, 32 at the nip 34.

First, the gap 34 provides a first gap line against which the web 20 can be broken. Other structures that provide the required gap can replace the web drive arrangement shown.

As shown in Fig. 2, the break bar assembly 16 includes break bars 52 mounted on first and second rotational members 54a, 54b. Although three break bars 52 are shown on each rotational member 54, a greater or lesser number of break bars 52 may be used.

In the breaker bar assembly 16, the drive device 56 drives a first drive belt 58 and a second drive belt 82. A transmission belt 62 drives a second drive belt 60 via the guide device 63. The guide device 63 preferably comprises a pulley or the like. The drive belt 58 thus drives the rotation member 54a in a counterclockwise direction while the drive belt 60 drives the rotation member 54a in a clockwise direction. Accordingly, the respective rotation members 54 drive the respective breaker bars 52 in closed paths and directed downward into cooperative and extending engagement with the track 20.

The drive of the rotary elements 54A and 54B is synchronized so that the breaker bars of the two rotary elements cooperatively, preferably simultaneously, grasp the web as shown in Fig. 2 to break the web at a corresponding line of weakness. While each When a pair of crowbars breaks the web at a line of weakness, the next pair of crowbars moves on rotating elements 54A, 54B to a "ready" position above the web.

When the web is broken, the rotating members stop rotating until again signaled by the controller 26 to rotate the next pair of breaker bars into engagement with the web. Thus, the rotating members 54A and 54B rotate intermittently in less than complete orbital increments to engage and break the web each time signaled by the controller 26. The controller 26 may issue such a signal at each detected line of weakness or after the detection of a predetermined number of lines of weakness.

The respective closed paths of the breaker bars extend across the width of the web. The drive device 56 provides incremental and intermittent drive of the belts 58, 80 and 82, and thus incremental and intermittent drive of the breaker bars 52 with the web breaking force directed downward against the web 20, breaking the web at respective lines of weakness.

While the belt 58 moves in a counterclockwise direction, the transmission belt 62, enabling a gear in the drive device 56, moves in a clockwise direction. The gear can be omitted and the belts 58 and 62 driven via a common drive pulley. The transmission belt 62 is then crossed between the drive device 56 and the drive device 63 as shown in Fig. 3 to obtain the correct direction of rotation on the guide device 63.

The rotation elements 54A, 54B preferably comprise pulleys or toothed pulleys, wherein the crowbars 52 of the pulleys or the sprockets. The leading edges of the breaker bars 52 grip the web. The leading edges typically define curved contours as opposed to sharp edges. In some embodiments, a sharp leading edge is acceptable, but generally a more curved contour is preferred.

Typically, the overall cross-sections of the breaker bars 25 are round or other curved shapes. Polygonal cross-sections and combinations of polygonal and curved cross-sections are also possible. A diameter of 15.9 mm (5/8") is preferred for the breaker bar 52, although other sizes and shapes may also work properly. The general requirement for breaker bars 52 is a cross-section with sufficient strength to stretch the web 20. The web is broken at lines of weakness that are offset from the contact lines between the breaker bars 52 and the web, with the breaker bars 52 having no sharp edges along all surfaces that contact the web.

The rotary members 54A, 54B support the breaker bars 52 in a common plane extending transversely to the web. The electrical controller 26 drives the rotary members 54A, 54B in opposite directions while synchronizing the rotation of the first and second rotary members 54A, 54B such that each corresponding breaker bar 52 on the first rotary member 54A is substantially aligned with and cooperates with a corresponding breaker bar 52 on the second rotary member 54B and transversely to the top of the web 20. Thus, the corresponding two operating breaker bars 52 (Fig. 2) on the top of the web 20 are aligned generally parallel to and transversely to the web upon initial engagement with the web. The operating breaker bars 52 define equal and opposite Angle "α" with the track at a first engagement with the track. The angles can be from zero (parallel to the track) to about plus or minus 20 degrees with respect to the track.

Prior to breaking the web, the breaker bars 52 preferentially grip the web 20 and apply a moderate tension which compensates for the slack without applying enough force to break the web. The controller 26 senses the speed of the web 20 entering gap 20 and the speed of the workpieces or bags exiting the gap via gap 38, calculates the amount of slack in the web material generated at any time, and the dynamic change in positions of the breaker bars required to compensate for the slack as the slack develops. The controller accordingly issues commands to the breaker bar drive which positions the breaker bars to compensate for the slack thus calculated.

In the take-up device 18, the drive device 70 drives a drive belt 92, thus driving the roller 66, which in turn drives the roller 64. The driven rollers 64 and 66 define the second gap 68. The web carrier belt 72 runs in a closed longitudinal path over the guide rollers 78, 80 and the driven roller 66. The web transport belt 74 runs in a closed longitudinal path over the guide roller 76 and the drive roller 64. The web carrier belts 72 and 74 are similar to the web carrier belts 44 and 46 of the web drive assembly 14.

The web carrier belt 72 is preferably a flat, full-width conveyor belt. The conveyor belt 72 transports workpieces separated from the web 20 to spindles 84, 86, 88 and 90 for winding. An air horn 96 operates with the spindle 90 to start winding the workpieces around it.

The electrical controller 26 controls the synchronization and operation of the elements of the web processing machine 10. Although a specific wind-up assembly 18 has been disclosed, other wind-up assemblies or web processing machines may be considered to be within the scope of the invention.

In Fig. 1, the carrier belts 44, 46 are shown as being cut between the nip 34 and the rollers 38, 40, which represents a preferred location where the web 20 breaks when stretched by the break bars 52. A trailing section 97 having a trailing edge 97A is shown as a first workpiece created by a break in the web 20, and a leading section 98 having a leading edge 98A is shown as a second upstream section which has not yet broken from the web and which will form the next subsequent workpiece when broken from the web, for example at the next line of weakness.

The term "bag" used throughout this disclosure is defined as a portion of the web between lines of weakness. The web 20 preferably comprises precursors of plastic bags of selected size. Preferably, the web and thus the bags are made of a plastic material or the like. However, the bags referred to herein may comprise other materials, such as sheets or films, which are not a bag in the traditional sense. Bags need not have an opening at any end or side.

The term "workpiece" as used herein is a section of the web 20 which results from the continuous web has been broken out or otherwise separated. Thus, in some embodiments of the application of this invention, a "workpiece" contains multiple "bags".

Each workpiece may comprise only one bag or a plurality of bags with unbroken lines of weakness between the bags. The plurality of bags may comprise any number of bags, such as 25, 50 or 100 bags, which may be wound on a spindle for storage or placement in a package, for example.

The invention works as follows. The web 20 is drawn into the tension roller assembly 12 by the tension at the nip 34. The tension roller assembly 12 thus receives the web 20 into the machine. In the tension roller assembly 12, rollers 22, 24 control the tension of the web 20. A position sensor (not shown) associated with the tension roller 24 sends position signals to the electrical control 26 to make permanent adjustments to the speed at which the web is drawn into the machine 10.

The breaker bars 52 generally do not cut the web. Referring to Figures 1-3, while the web is firmly grasped at the gap 34, the leading edge of the web enters the gap 68. While the web is firmly held or anchored in both gaps 34 and 68, the breaker bars 52 travel downward against the top of the web, exerting a tensile stretch on the web, and breaking the web at a line of weakness between the first and second gaps, preferably between the first gap 34 and the breaker bar assembly 16.

Although the drive belts 58, 60 and 62 preferably comprise synchronous belts, a variety of other structures can be proposed to replace the drive belts. For example, individual drive motors, which are driven by the controller 26, provide the same function.

The weak line sensor 28 provides a signal to the controller 26 when each weak line is detected. From the tension roller assembly 12, the web 20 follows a path between the carrier belts 44, 46 from the nip 34 to the rollers 38, 40.

The controller 26 controls the breaker bar assembly 16, which moves the breaker bars 52 downward to break the web 20 after the detected line of weakness passes the first nip 34 and preferably before the line of weakness reaches the rollers 38 and 40. Breaking the web produces a workpiece having a trailing portion 97 having a trailing edge 97A and a leading portion 98 on the remainder of the web having a leading edge 98A. Breaking the web 20 is repeated at selected spaced lines of weakness in response to successive signals from the controller 26. In some embodiments, the breaker bars 52 are advanced to break the web only when a predetermined number of lines of weakness have been detected.

The second nip 68 continues to pull the broken workpiece therethrough, with the workpiece being guided by the web carrier belts 72 and 74 to the turret assembly 82. An air horn 96 cooperates with the turret assembly 82 and the spindles 84, 86, 88 and 90 to wind the leading edge of the corresponding bag or workpiece onto the corresponding spindle. After the leading edge of the first workpiece(s) to be wound onto that spindle has been secured onto the spindle (e.g., spindle 84), the turret assembly rotates as the spindle winds up the web, respectively, winding up the next spindle (e.g., spindle 86). B. the spindle 90) into the position shown in Fig. 1.

In a continuous mode of operation, the web 20 is preferably wound up as a roll of bags connected together by spaced lines of weakness. Winding continues until the trailing edge 97A of the last bag to be wound onto the roll is wound. The electrical controller 26 controls the winder 18 so that the leading edge 98A of the next group of bags is then wound around the spindle near the air horn 96, and then the turret assembly 83 rotates again. The selected spindle 84, 86, 88 and 90 with the fully wound roll rotates with the turret assembly to the next position. An ejector assembly (not shown) removes the wound roll of bags from the selected spindle. In this continuous mode of operation, a web 20 is broken at a line of weakness when a preferred number of lines of weakness have been detected by the sensor 28. The predetermined number of lines of weakness corresponds to a corresponding preselected number of bags. In this mode of operation, the preselected number of bags are wound onto a first spindle and then another group of bags, typically the same number, are continuously and sequentially wound onto a subsequent spindle.

In the continuous mode of operation, the wind-up assembly 18 preferably operates at substantially the same speed as the web drive assembly 14. This avoids slack in the web 20 passing the crowbar assembly 16.

In a layering mode of operation, the sensor 28 detects each line of weakness and the controller 26 controls the crowbar assembly 16 to break the web into individual workpieces by breaking the web at each line of weakness. The nip 68 pulls the web at a slower speed than the web drive assembly 14, thereby creating a slack in the web 20 as the web traverses the gap "G" (shown in Figs. 1 and 5).

The breaker bar assembly 16 takes up the slack created by the speed difference by bringing the respective breaker bars 52 into engaging contact with the web by applying a moderate force sufficient to take up and continue to take up the accumulating slack, but not sufficient to break the web at the incoming line of weakness. At the correct time, the force is quickly increased sufficiently to break the web at the corresponding line of weakness. This process is repeated at each line of weakness.

As the trailing edge 97A of the leading workpiece moves downward to a lower position between the nips 34 and 68 due to the combination of gravity and the downward breaking force, the leading edge 98A of the remainder of the web 20 passes the rollers 38, 40 and over the trailing edge 97A, sandwiching the leading edge 98A over the trailing portion 97. The remainder of the web that lies above the trailing portion 97 depends on the difference in drive speeds at the nips 34 and 68. Increasing the difference in speed increases the amount that the web 20 lies above the leading workpiece. The wind-up assembly 18 then pre-winds the sandwiched workpieces into a roll on the spindle 84, 86, 88 or 90 as described above.

The electrical controller 26 may comprise a computer, a microprocessor or other electronic device which can control the web processing machine 10. Further, the electrical controller 26 may also include an analog electrical circuit which receives the input signals from the sensor 28, the tension roller 24 and other elements while controlling the drive devices 48 and 70, the breaker bar assembly 16, the turret device 82 and the air horn 96 and other elements of the web processing machine 10. The controller 26 may take other forms. For example, the controller 26 may be a pneumatic or hydraulic controller using corresponding pneumatic or hydraulic logic and control devices.

Fig. 3 illustrates another embodiment of the breaker bar assembly 16, which includes first and second drive belts 99, 100 and breaker bars 52. The drive device 56 may comprise a servo motor, a standard AC motor, and the like. The drive device 56 supplies power to the drive device 63 via a crossed transmission belt 82. Respective drive belts 99 and 100 are supported along their respective paths by respective first and second guide devices 102 and 104 in combination with the drive device 56 and the drive device 63. The guide devices 102 and 104 typically comprise pulleys, gear pulleys, or the like.

The drive belts 99 and 100 preferably comprise synchronous belts or the like. The breaker bars 52 are fixedly mounted on the respective drive belts and extend outwardly from the drive belts 99 and 100 as shown in Fig. 3. The breaker bars 52 are driven in a downward direction to break the web 20. By breaking the web 20 in a downward direction, the rear Edge 97 of a first workpiece is pressed downwards into a position below the gaps 34 and 68. The front edge 98A of the remainder of the web runs in a straight line extension of the belts 44, 46 from the rollers 38, 40, and thus runs over the rear edge 97A. This results in an effective layering of the front edge 98A over the rear portion 97.

Further, as shown in Fig. 3, two breaker bars 52 are shown on each drive belt 99 and 100. A greater number could be used. The breaker bars 52 are guided by the drive belt 99 along its entire closed path via the guide device 102 and the drive device 56 for engaging the web 20 in a downward translation direction. The drive device 56 drives the drive belt 99, which is preferably a synchronous belt, along the closed path which includes the above guide device 102. Major portions of the elongated path extend in a straight line substantially perpendicular to the direction of travel of the web. The drive belt 100 and corresponding breaker bars 52 operate in substantially the same manner and are located in a common plane with the breaker bar 52 on the first drive belt 99. The longitudinal paths of the first and second drive belts 99 and 100 are preferably identical in size and shape.

In operation, as shown in Fig. 3, the electrical controller 26 drives the belts 99 and 100 in opposite directions, shown by arrows, and thus controls the forward movement of the breaker bars 52 along first and second paths substantially perpendicular to the direction of travel of the web. Thus, the respective breaker bars 52 are oriented substantially transversely to the top of the web before they engage and break the web. The breaker bars 52 preferably take up the slack in the web 20 by applying a constant take-up force by taking up and holding the slack in the web after the leading edge 98A is engaged in the gap 68 and before they operate to break the web 20.

In Fig. 3A, breaker bars 52 are mounted only on the left drive belt 100 and extend completely across the width of the track to the right drive belt 99. The right drive belt 99 has receptacles 101 which are cooperatively spaced with respect to the spacing of the bars 52 on the drive belt 100.

Both belts 99 and 100 are driven at a common speed, with cooperative synchronization such that as each breaker bar moves around a pulley 104 and extends across the track 20 to the belt 99, a receiver 101 on the advancing belt 99 comes into alignment with the breaker bar and momentarily receives, supports, and preferentially locks the distal end of the breaker bar away from the belt 100. Thus, each breaker bar 52 is permanently secured to the belt 100, and is temporarily secured and secured to the belt 99 as the track-breaking portion moves downward on its orbital path. The distal end of the breaker bar is released from the corresponding receptacle 101 at the end of each downward portion of the path, after which it travels around the drive device 63 and along the upward portion of the orbital path back to the pulley 104.

Locking the crowbar means restraining the crowbar at least with respect to movement (e.g. upward or downward) toward or away from the surface of the web engaged by the crowbar.

Thus, in the version of Fig. 3A of this embodiment, each crowbar is permanently attached to only one of the belts 99, 100. The permanent attachment can of course be made to any such belt with receptacles 101 attached to the other belt.

As in other embodiments of this invention, the drive of the breaker bars is preferably intermittent and incremental along the respective orbital paths under control of the controller 16.

Fig. 4 illustrates a side view of the break bar assembly 16 of Fig. 4 in the web processing machine 10. Referring to Figs. 1 and 2, in this embodiment the length of the gap "G" between the rollers 38, 14 and the nip 68 is less than 12.7 cm (5"), preferably less than 7.6 cm (3"), more preferably about 2.5 to 5.1 cm (1 to 2") or less. The web 20 is unsupported across the gap "G".

As the web extends across the gap, gravity pushes the unsupported front portion 98 of the web downward. The inherent stiffness of the web tends to keep the front portion 98 in a straight line, generally horizontal direction. The longer the unsupported length of the web across the gap "G", the greater the gravity effect. Thus, the longer the gap, the greater the possibility of gravity overcoming the inherent stiffness of the web, pushing the web downward so that the web is not properly inserted into the gap 68. However, the compact length of the crowbar assembly 16 of the invention and the corresponding reduced length of the gap "G" reduces the distance the web travels unsupported and thus the effect of gravity on the unsupported supported web. Since the web traverses the shorter gap "G" in the invention rather than the relatively longer gaps of the prior art machines, there is less chance of web mistracking due to the web 20 bending downward while traversing the gap "G". Thus, the web processing machine 10 has greater reliability than prior art web processing machines.

In practice, because of the reduced length of the gap "G", gravity imposes only nominal practical limitations on the gap "G" in web manufacturing processes typically used to make plastic bags of about 0.013 to 0.05 mm (0.5 mil to 2.0 mil) thickness of plastic web. The shorter gap "G" thus makes the machine 10 more versatile in that it can handle thinner webs through the gap "G".

Fig. 5 illustrates a side view of a fragment of the web processing machine 10 which includes a third embodiment of a breaker bar assembly 16 having two breaker bars 52A, 52B which engage the web at spaced locations along the length of the web to tension and then break the web. As shown in Figs. 5 and 6, breaker bars 52 are mounted on drive belts 105 and 116 adjacent first and second edges 120A and 120B, respectively. The drive belt 105 is mounted on a drive device 108 and a guide 110. The guide device 110 and the drive device 108 are preferably toothed pulleys, belt pulleys or the like driven by a servo motor, standard AC motor or the like. Locations 112 and 114 show the positions corresponding crowbars 52 in a rest position before they are moved into engagement with the track.

The drive belt 116 is mounted on the second drive device 126 and the guide device 118. The drive belts 105 and 116 are arranged in the web processing machine 10 adjacent to the respective edges of the web. First ends of the breaker bars 52 are attached to the drive belt 105. Second ends of the breaker bars 52 are attached to the drive belt 116.

Carrier belts 44, 46 are removed between the nip 34 and the rollers 38, 40 and show where the web 20 breaks when it is gripped and stretched by the breaker bars 52. The drive belts 105 and the guide device 110 are disposed in a first generally planar surface adjacent and extending generally along the edge 120A of the web 20. Similarly, the drive belt 116 and the guide device 118 are disposed in a second generally planar surface adjacent and extending generally along the edge 120B. See Fig. 6.

Referring to Figures 5 and 6, the take-up assembly 18 includes a nip subassembly 122 which forms a nip 68 which securely grasps and holds the web 20 after the leading edge of the remainder of the web crosses the gap "G". The nips 34 and 68 provide nip anchor points against which the breaker bars 52 break the web.

In operation, the breaker bar 52A closest to the guide rollers 38 and 40 moves upwardly in a straight line direction along the first path segment 106, while the second breaker bar 52B moves in a straight line direction along a second path segment 110 into no more than a slight stretching engagement with the web 20, which takes up the slack. The directions of movement along the path segments 106 and 107 are represented by arrows 115. This movement of the first and second breaker bars 152 takes up the slack in the web 20 by simultaneously deflecting the web in upward and downward directions. The breaker bars 52 continue to move in the given directions, continuing to take up the slack as the web is fed further through the gap. At the appropriate time, and under the control of the controller 26, the breaker bars 52 break the web 20 by momentarily making a step-like increase in their speed of travel along the path. The break creates a trailing edge 97A of a first (leading) workpiece and a leading edge 98A of a second (trailing and still to be separated from the web) workpiece.

After breaking the web, the breaker bars 52 move into the rest positions, which are shown for example at 112, 114 in Fig. 2, and wait here until the newly formed front edge 98A passes through the gap again and enters the gap 68. The control then signals the breaker bars again to take up the slack and then break the web as described above.

As can be seen in Fig. 5, the first path segment 106 comprises the straight line traversed upwards by the drive belt 105 from the right edge of the drive device 108 to the right edge of the guide device 110. Similarly, the second path segment 110 comprises the straight line traversed downwards by the drive belt 105 from the left edge of the guide device 110 downwards to the left edge of the drive device 108. The first and second straight path segments 106 and 107, in combination with the curved segments around the drive device 108 and the guide device 110, form a single elongated closed path. The breaker bars 52 generally move along the elongated closed path in a rectilinear direction before engaging the web 20, while engaging the slack, while breaking the web, and after the web 20 breaks. The breaker bars, of course, traverse the curved portions of the path around the drive assembly 108 and the guide assembly.

The respective straight line segments 106, 107 of the first and second paths are disposed between respective outer edges of the drive device 108 and the guide device 110. Each such straight line segment is at least 10 cm (4") in length. Preferably, each such straight line path segment (106 and 107) is 20 to 25.4 cm (about 8 to about 10") long. Longer path segments are permissible.

The lateral spacing "S" (Fig. 5) of the first path segment 106 from the second path segment 107 is a distance of no more than 3.8 cm (1.5"), preferably between 0.63 and 2.64 cm (0.25 and 1"). There must, of course, be sufficient clearance between the path segments to allow the crowbars 52 to pass one another without intervening contact as they travel along the elongated portion of the closed path.

Although Fig. 5 only shows two breaker bars attached to the drive belt 105, more are conceivable. Any number of breaker bars 52 can work as long as they are spaced appropriately between the operating pairs of bars 52. Namely, the spacing between bars 52 must be sufficient that a subsequent pair does not interfere with the feeding of the leading edge 98A of the web across the gap "G". In addition, the distance from the Gap 68, transverse to rod 52B to drive device 108, must be long enough so that front edge 97A is not caught by drive device 108.

Elements of the second guide device 118 preferably correspond to the elements specified for the first guide device 110. The second drive belt 116 is driven by the first drive device 108 via a drive shaft 119. The first and second drive belts 105 and 116 are thus driven at a common speed in such a way that each breaker bar 52 always covers the entire width "W" of the web at once.

Fig. 6A illustrates a preferred arrangement of a drive shaft 119. As seen therein, the drive shaft 119 is driven by the transmission shaft 128 through a suitable coupling (not shown). Spaced apart pulleys 130, 132 are mounted on and drive the drive shaft 119. The pulleys 134 and 136 are mounted adjacent to the respective drive devices 108, 126 and are connected thereto through stub shafts 138. Drive belts 140 connect the pulleys 130, 132 to the pulleys 134, 136, respectively. When the transmission shaft 128 rotates, it causes rotation of the shaft 119. Rotation of the shaft 119 causes rotation of the pulleys 130, 132, driving the belts 140, the pulleys 134, 136, the stub shafts 138, and therefore the drive device 108 and 126.

Fig. 6 illustrates the guide roll 38 and the driven roll 30 but no web carrier belt 44 or guide roll 36 to show a line of weakness 121 at a location which is preferably occupied by each line of weakness when the web is broken. The line of weakness 121 may include perforations, slits, weakened portions which are not cut through or the like. The line of weakness 121 extends completely across the web 20 in a direction transverse to the path of travel of the web 20. The line of weakness 121 is preferably located at the position shown in Fig. 6, or even closer to the drive roller 30 when the web is broken by the action of the breaker bars 52.

In the stratification mode of operation, as the breaker bars 52 break the web 20, the downstream breaker bar 52 pulls the leading edge 97A of the trailing portion 97 of the workpiece downward from the gaps 34 and 68. The leading edge 98A extends beyond the trailing edge 97A and overlies the trailing portion 97. The trailing edge 97A and leading edge 98A are then pulled together through the second gap 68 and then to the take-up turret assembly 82.

Fig. 7 illustrates a plan view of another embodiment of the invention, similar to that of Figs. 5 and 6. Drive belt 105 carries at least two breaker bars 52. Drive belt 116 carries at least two breaker bars 52. Respective breaker bars 52 on drive belts 105, 116 are in alignment with one another substantially transverse to the web, much as in the orientation discussed above with reference to Figs. 2, 3 and 6. The selected breaker bars 52 of each respective drive belt 105, 106 move in respective up and down rectilinear directions before, during and after contact with the web. The path segments traversed by the crowbars 52 on the belts 105 and 116 as the bars pass through the drive device 56, guide device 102, drive device 63 and the guide device 104 comprise a pair of elongated closed pairs as shown in Fig. 5 and 6. The paths are similar in size and shape and are adjacent to the respective first and second edges 120A, 120B of the track 20. Thus, the breaker bars 52 on the first drive belt are aligned with the breaker bars on the second drive belt. The embodiment of Fig. 7 is similar to the embodiment of Figs. 5 and 6 with the exception of the free ends 123, 124 of the breaker bar 52 in the middle of the width "W" of the track 20.

8A and 8B illustrate another embodiment of the breaker bar assembly 16. Referring to FIGS. 8A and 8B in combination, the breaker bar assembly 16 includes first and second belt support assemblies 143A and 143B. In the belt support assembly 143A, pulleys 142A, 142B, 142C and 142D define a first rectangular orbital path traversed by an endless belt 114 and defined in a first receiving plane, such as plane "P1". In the belt support assembly 143B, corresponding pulleys 146A, 146B, 146C and 146D define a second rectangular orbital path traversed by an endless belt 148 and defined in a second receiving plane, such as plane "P1". B. the plane "P2" is defined parallel to the plane "P1".

The belt support assemblies 143A and 143B are separated from each other by a gap "SP" and laterally offset from each other. The belt support assembly 143 circumscribes the width of the track 20. The belt support assembly 143A is laterally offset from the track 20, as well as offset along the length of the track from the track support assembly 143B.

Each breaker bar 52 is mounted on both belts 144 and 148 for an articulated connection with respect to both belts. As can be seen in Fig. 8A, the lengths of the bars 52 are parallel to the belts 144 and 148 and planes "P1"and"P2" and are positioned between the planes "P1" and "P2". The drawings show two crowbars 52A, 52B. The number of crowbars can be selected according to the application requirements of a specific web processing machine 10.

Figure 8B illustrates a preferred path of travel of the breaker bars in the breaker bar assembly. As shown, breaker bar 53A is positioned adjacent to belt support assembly 143A and will subsequently move in an upward direction as shown by arrows 150. The right end of bar 52A is attached to belt 144. The left end of bar 52A is attached to belt 148. Breaker bar 52B is positioned adjacent to belt support assembly 143B, is positioned near the top of track 20 and will subsequently move in a downward direction as shown by arrows 152. The right end of bar 52B is attached to belt 144. The left end of bar 52B is attached to belt 148. Accordingly, the breaker bar 52A extends across a first opening 154A defined between the legs 156A of the straps 144, 148 along the right-hand portions of the corresponding paths, and the bar 52B extends across the second opening 154B defined between the legs 156B of the straps 144, 148 along the left-hand portions of the corresponding paths.

The controller 26 controls a suitable drive mechanism (not shown) which drives the belts 144, 148 simultaneously so that the belts 144, 148 are driven at a common speed about their respective orbital paths. Fig. 8B illustrates that projections of the orbital paths defined by the belts 144, 148 overlap at the pulleys 142A, 142B, 146C and 146D. Although such overlap is not required, the overlap is desirable for reasons of compactness of the assembly 16.

According to the structure described above and beginning with the position of the breaker bar 528, driving the belts 144, 148 brings the breaker bar down into the opening 154B, engaging and breaking the web 20. When the breaker bar reaches the bottom of the opening 154B, the belts 144, 148 transport the ends of the bar around the pulleys 142a and 146a and move the bar laterally along the lower segments 158A, 158B of the paths traversed by the belts 144, 148 to the opening 154A. The bar then travels upwardly in the opening 154A and is transferred laterally along the upper segments 160A, 160B of the paths by the belts 144, 148 to the opening 154A. Back in the opening 154A, the breaker bar again travels downwardly, again breaking the web at a subsequent line of weakness 121. It will be clearly seen that the belt 148 runs around the gap "G" and does not have to pass through the gap "G".

Thus, each breaker bar travels along a circular path down in the opening 154B, laterally to the right from the opening 154B to the opening 154A, upward in the opening 154A, laterally to the left from the opening 154A to the opening 154B, and then again downward in the opening 1548. The illustrated breaker bar 52B illustrates a downward movement in the opening 154B. The illustrated breaker bar 52A illustrates an upward movement in the opening 154A. Arrows 162 illustrate the travel paths of the belts 144, 148. During the entire travel along its circular path, each breaker bar maintains its, for example, parallel, orientation with respect to the surface of the web 20.

Major advantages of the embodiment of Figs. 8A and 8B are that (1) both ends of the respective breaker bars are secured in the breaker bar assembly, resulting in the strength and control inherent in securing both ends, and (2) the length of the breaker bar assembly along the gap "G" can be limited to a gap limited by only a single breaker bar at the opening 154B and no additional length need be provided in relation to the belt 148 or any other drive element. This embodiment thus provides the breaker bar with the strength and control advantages of the embodiment of Fig. 5, securing both ends of the breaker bars when breaking the web in combination with the minimal gap lengths of, for example, embodiments such as those shown in Figs. 1 to 3.

If it is desired to provide an upstream breaker bar 52A and a downstream breaker bar 52B to cooperate in an upward and downward driving engagement with the web in Fig. 5, a pair of breaker bar assemblies 16 of Figs. 8A and 8B may be used. Namely, a second such breaker bar assembly 16 may be added to the structure upstream (with respect to the web passage) of the illustrated assembly and with the web extending through the opening 154A, with the breaker bars of the second breaker bar assembly traveling in an upward direction to engage the web while the breaker bars in the first breaker bar assembly traveling in a downward direction to engage the web.

Throughout the foregoing disclosure, the invention has been illustrated with a horizontal track 20 and a downward movement of the breaker bars 52 into a breaking engagement with the track. In the embodiments of Figs. 5 to 7, the breaking engagement includes a second upwardly extending the breaking engagement comprises a second upwardly moving breaking bar which cooperates with the downwardly moving breaking bar in breaking the web.

The actual orientation of the web with respect to the horizontal is not limited to that shown. For example, the web breaking operation can be satisfactorily performed on an upwardly or downwardly inclined web, including a vertically (either upwardly or downwardly) running web or on a web which runs on an edge, such as when the edge 120B is vertically or at an angle above or below the edge 120A.

Likewise, breaking the web need not be accompanied by any downward movement of a crowbar. Instead, it is important that proper provision be made only to guide the leading edge 98A of the remainder of the web across the gap to the nip 68, and to properly orient and position the leading portion with respect to the trailing portion 97 when operating in the layering mode. Preferably, the trailing edge is generally pushed upwardly or sideways when broken from the web. However, due to the short length of the gap "G" and the correspondingly limited defect in gravitational forces, upward pushing operations can also be tolerated.

Those skilled in the art will now appreciate that certain modifications may be made to the devices and methods disclosed herein with reference to the illustrated embodiments without departing from the scope of the invention as claimed. Moreover, since the invention has been described above with reference to the preferred embodiments, it will be understood that the invention is capable of numerous rearrangements, modifications and changes and that all such arrangements, modifications and changes are intended to be within the scope of the appended claims.

Claims (11)

1. An apparatus (10) for breaking a continuous web of material (20) during movement of the web at lines of weakness (121) extending transversely to the width (W) of the web (20), the lines of weakness (121) being spaced along the web (20), the apparatus (10) comprising first and second driven rollers (30, 32) defining a first nip (34) for receiving and transporting the web (20) therethrough, third and fourth rollers (64, 66) defining a second nip (68) for receiving and transporting the web (20), and a controller (26) for controlling the drive of the web (20) through the first nip (34) and the second nip (68), the apparatus (10) being characterized by: a breaker bar assembly (16) disposed downstream of the first gap (34) and upstream of the second gap (68), the breaker bar assembly (16) including at least one breaker bar (52) extending substantially transversely to the width of the web (20), and the drive device (56) of the breaker bar assembly (16) bringing the at least one breaker bar (52) into breaking contact with the web (20), the at least one breaking bar (52) having a generally arcuately shaped cross-section with a leading edge free of sharp edges for contact with the web (20) at a line of contact offset from the first line of weakness (121) and operable to break the web (20) during movement the track breaks at the corresponding lines of weakness shifted from the lines of crowbar contact. 2. Device (10) according to claim 1, which further comprises a first rotation element (54A; 104; 118; 146B) which is connected to a first belt (60; 100; 116; 148), wherein the at least one breaker bar (52) is mounted on the first rotation element (54A; 104; 118; 146B) or the first belt (-; 100; 116; 148). 3. Device (10) according to claim 2, which further comprises a second rotation element (54B; 102; 110; 142D) which is connected to a second belt (58; 99; 105; 144), wherein the at least one breaker bar (52) is mounted on a second rotation element (54B; -; -; -) or the second endless belt (-; 99; 105; 144). 4. The apparatus (10) of claim 3, wherein the at least one breaker bar (52) comprises at least first and second breaker bars (52) which are rotatable in clockwise and counterclockwise directions with respect to each other, respectively, in cooperative and stretching engagement with the track (20) on the first and second rotation members (54A, 54B) so as to contact the track (20) at an angle (α) of between ±20° to the track (20), defining 0° when the breaker bars are parallel to the track (20). 5. The device (10) of claim 1, further comprising a rotation element connected to a first belt and a second rotation element connected to a second belt, and wherein the at least one breaker bar (52) has a first end attached to one of the first belt (105; 99; 144) and the second belt (116; 100; 148). 6. The apparatus (10) of claim 5, wherein the at least one breaker bar (52) comprises at least first and second breaker bars (52) such that the second end of the at least first breaker bar (52) is attached to the first endless belt (100) and the second end of the at least second breaker bar (52) is attached to the second endless belt (99), and the at least first and second breaker bars (52) are rotatable on the first and second belts (100, 99) in identical elongated paths relative to each other on the first and second belts (100, 99) and through the track (20). 7. The apparatus (10) of claim 5, wherein the other of the first belt (100; 116; 148) and the second belt (99; 105; 144) has receptacles (101) that temporarily receive and support a distal end of the at least one breaker bar (52) during movement of the at least one breaker bar (52) into breaking contact with the web. 8. The apparatus (10) of claim 3, wherein the at least one breaker bar (52) includes first and second breaker bars (52A, 52B), the first and second breaker bars (52A, 52B) each having first and second ends, the first ends of each of the first and second breaker bars (52A, 52B) being attached to the first endless belt (110, 144), and the second ends of each of the first and second breaker bars (52A, 52B) being attached to the second endless belt (105, 148) such that the first and second breaker bars (52A, 52B) move up and down in cooperating paths and simultaneously deflect the web (20) both up and down and break the web at a corresponding line of weakness. 9. The apparatus (10) of claim 3, wherein the at least one breaker bar (52) comprises first, second, third and fourth breaker bars (52), each having first and second ends, the first ends of each of the first and second breaker bars (52) being attached to the first endless belt (99, 116), the third and fourth breaker bars (52) being attached to the second endless belt (100, 105), the second end of the first breaker bar (52) being aligned with the third breaker bar (52), and the second end of the second breaker bar (52) being aligned with the second end of the fourth breaker bar (52) such that the first and third breaker bars (52) move downwardly toward the web (20) while the second and fourth breaker bars (52) move upwardly toward the web (20), and thus the Track (20) breaks at a corresponding line of weakness (121). 10. The device (10) of claim 3, wherein the at least one breaker bar (52) has a first end attached to the first endless belt (148) and a second end attached to the second belt (144), the at least one breaker bar (52A) being movable in a closed circuit path, the first belt circumscribing and traveling along a path traversed by the web (20), and the second belt traveling along a path laterally offset from the path traversed by the web (20). 11. A method for breaking a continuous web of material (20) during movement of the web at lines of weakness (121) extending transversely to a width (W), wherein the lines of weakness are spaced along the length of the web (20), and the method comprises: Providing an apparatus (10) including first and second driven rollers (30, 32) defining a first nip (34) for receiving and transporting the web (20) therethrough, third and fourth rollers (64, 66) defining a second nip (68) for receiving and transporting the web (20) through the second nip (68), and a controller (26) for controlling the driving of the web (20) through the first nip (34) and through the second nip (68), the method being characterized by: Providing a breaker bar assembly (16) having at least one breaker bar for breaking the web (20) at a corresponding line of weakness (121), the breaker bar assembly (16) being arranged downstream of the first gap (34) and upstream of the second gap (68); Providing at least one breaker bar (52) extending substantially across the width of the web (20) and being displaceable relative to the web to break the web (20) at the corresponding break line (121), the at least one breaker bar (52) having a generally arcuately shaped cross-section with a leading edge free of sharp edges for contact with the web (20) at a contact line displaced from the first line of weakness (121); Activating the drive device (56) of the breaker bar assembly (16) to bring the at least one breaker bar (52) into contact with the web (20) so that the leading edge of the at least one breaker bar (52) which is free of sharp edges cuts the web at a position displaced from the corresponding line of weakness (121) contact line and thereby breaks the web (20) during the movement of the web at the contact line displaced from the corresponding line of weakness.